In a small sauce pan put 3/4 cup of sugar and cover the sugar with a little bit of water until the sugar looks like wet sand.
Cook on a stove top over high heat until it reaches 248 degrees.
While the sugar is cooking, whip eggs whites in a bowl of an electric mixer fitted with the whisk attachment at a high speed until they reach soft peaks.
Once the egg whites reach soft peaks add the other 1/4 cup of sugar and mix on a high speed until the egg whites reach stiff peaks.You can keep mixing the egg whites at a high speed until the sugar is done cooking.
Once the sugar reaches 248 degrees, and the mixer is on high, add sugar mixture to the egg white mixture.
Mix on a high speed for 30 minutes.
After 30 minutes, add the room temperature butter and mix on a high speed for 5-10 minutes until the butter is fully combined and the mixture resembles buttercream.
Add vanilla and mix until just combined.